Photographic silver halide emulsion containing finely divided uinert particles dispersed in a synthetic colloid medium and a silver halide developer



United States Patent Ofiice 3,352,682 Patented Nov. 14, 1967 3,352,682 PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINHNG FINELY DIVIDED INERT PARTICLES DISPERSED IN A SYNTHETIC COLLOID MEDIUM AND A SILVER HALIDE DEVELOPER Albert Edward Harris and Edward Cyril Dodd, Ilford, England, assignors to Ilford Limited, llford, England, a British company No Drawing. Filed Sept. 9, 1964, Ser. No. 395,319 Claims priority, application Great Britain, Sept. 13, 1963, 36,192/ 63 1 Claim. (Cl. 9695) ABSTRACT OF THE DISCLOSURE Photographic material which comprises a film support and a layer of a gelatino silver halide photographic emulsion, the emulsion containing (1) a photographic developer, notably hydroquinone, and (2) finely divided particles of a photographically inert substance, particularly silica, dispersed in polyvinyl alcohol, i.e. a synthetic colloid medium compatible with gelatin.

This invention relates to novel photographic materials and to their use.

A known process for the production of photographic records makes use of a light-sensitive material which comprises a sheet support carrying a layer of gelatino silver halide photographic emulsion which includes a developing agent for the silver halide. In use such a material is imagewise exposed to form a latent image and then processed by contacting it first with a so-called activator solution, which is a solution containing alkali which serves to activate the developer in the emulsion, and then with a socalled stabiliser solution which is a solution which contains a substance, usually a water-soluble thiocyanate, which forms a complex with the residual silver halide, rendering it non-light sensitive. In this way a photographic print of a high degree of stability may be readily and rapidly obtained.

In practice it is convenient to pass the exposed photographic material through a roller system which applies the activator and stabiliser solutions successively as thin liquid films to the surface of the material and in this form the process is of considerable convenience as a means for document reproduction.

Usually the sheet material on which the photographic emulsion is coated is paper and since this is an absorbent material the salts formed in the emulsion layer during processing are partially absorbed into the paper base. However, if the same procedure is attempted using a photographic material in which the developer-containing emulsion is coated as a layer on a film base, e.g. a base of cellulose triacetate, cellulose acetate-butyrate, polystyrene, a polyethylene terephthalate, a polycarbonate or like film material, this absorption cannot take place and, accordingly, there is a tendency for salts formed during processing to crystallise out on the surface of the material when it is dry, a circumstance which is deleterious to the quality of the product.

It is an object of the present invention to provide a new form of photographic material of which the base support is sheet film and which avoids the defect referred to above, and to provide a process for the use of such material for the production of photographic records.

According to a first feature of the present invention there is provided a photographic material which comprises a film support and a layer of a gelatino silver halide photographic emulsion, the said emulsion containing (1) a photographic developer compound and (2) finely divided particles of a photographically inert substance dispersed in a synthetic colloid medium compatible with gelatin. In a preferred form of the material the finely divided material is silica and the synthetic colloid medium in which such particles are dispersed is polyvinyl alcohol.

According to a still further preferred form of the material the side of the film support opposite to that which carries the photographic emulsion is itself provided with a layer comprising particles of a photographically inert material in a medium of gelatin and synthetic colloid, preferably finely divided silica in a medium of gelatin and polyvinyl alcohol.

The film support may be a film of any of the materials referred to above as suitable for the purpose, or any other known per se for use with photographic materials. It is preferably colourless, clear and of thickness three to five thousandths of an inch,

The photographic emulsion may be any gelatino silver halide emulsion known per se for use in a process of the type in which the emulsion contains a developing agent and is processed by treatment with activator and stabiliser as aforesaid. The developer used is preferably hydroquinone.

The particulate material used must be of very small particle size and, typically, silica of particle size 2 to 3 microns is very suitable. The silica is dispersed in the colloid medium such as polyvinyl alcohol and the dispersion added to the photographic emulsion, preferably in such quantity that it will give, when the emulsion is coated, a silica coating weight of 0.4 to 0.6 grams per square metre of coating. Its concentration in the dispersion may be, conveniently, from 612% by weight, e.g. an 8% by weight dispersion of silica in a 10% by weight aqueous solution of polyvinyl alcohol.

The backing of the film support (when a backing is used, as is preferable) conveniently consists of a similar dispersion of silica in polyvinyl alcohol, added to a gelatin solution of gelatin concentration comparable to that used in the photographic emulsion, and is applied to give a similar silica coating weight and similar or slightly greater gelatin coating weight.

The new photographic materials may be processed using activator and stabiliser solutions known per se. The activator solution preferably consists of an aqueous solu tion of sodium hydroxide at 5-8% concentration (preferably 6%) and containing 340% alkali metal sulphite (preferably 5% sodium sulphite). The stabiliser solution is preferably an aqueous solution of a water-soluble thiocyanate, preferably ammonium thiocyanate but it is found that it is generally sufiicient to provide a solution of much less thiocyanate content than is commonly optimal when treating a photographic material of the same type coated on paper base.

The following example will serve to illustrate the invention:

EXAMPLE A photographic emulsion is prepared by a conventional technique which contains 1000 g. of silver as silver halide, 540 g. of hydroquinoue, 5000 g. of gelatin and an 8% by weight suspension of very finely divided silica in a 10% by weight aqueous solution of polyvinyl alcohol is prepared and is added to the emulsion to provide 370 g. of silica in the emulsion.

The resulting emulsion is coated on film base at a coating weight of 1.2 g. silver/square metre which provides a silica coating weight at 0.44 g./square metre.

The photographic film thus obtained is imagewise exposed, and treated with an activator solution which is a 6% by weight aqueous solution of sodium hydroxide con- 3 taining 5% by. weight of sodium sulphite. The film is then treated in a stabiliser bath of the formula:

Ammonium thiocyanate g 125 Sodium metabisulphite g 35 Sodium acetate g 20 Acetone ml 50 l-phenyl-S-mercapto tetrazole g 2 Ethanol ml 200 Acetic acid 1 6 to 8 Water to make 1 litre.

Enough to bring pH of final composition to 4.9 to 5.1.

dimercapto 1,2,4-oxadiazoles, Z-mercapto benzthiazole and like compounds.

These compoundscan alternatively or in addition be included, as their metal salts which are insoluble in water but soluble in the stabiliser solution, in the photographic.

emulsion itself.

It is to be understood that while the synthetic colloid medium used to disperse the inert substance in the pro ducts of the invention is preferably polyvinyl alcohol because that substance is most readily available, nevertheless the invention is not confined to the use of polyvinyl alcohol; any water-soluble or water-dispersible synthetic colloid which is compatible with gelatin can be employed and commerce provides a wide choice of such materials.

Further, instead of using silica any other inert finely divided materialmay be employed e.g. other oxides such as alumina, titania, insoluble starch and its water-insoluble derivatives.

We claim as our invention:

A photographic material which comprises a film support anda layer of a gelatino silver halide photographic emulsion, the said emulsion containing (1) hydroquino'ne and (2) finely divided silica dispersed in polyvinyl alcohol, the silica being present in 'a proportion suflicient to provide 0.4 to 0.6 g. of silica per square metre of the emulsion layer.

References Cited UNITED STATES PATENTS 2,989,417 6/196'1 Overman 106-135 3,257,205 6/1966 Cassiers et al. 9629 FOREIGN PATENTS 1,174,157 7/1964 Germany.

NORMAN G. TORCHIN, Primary Examiner. J. TRAVIS BROWN, Examiner.

C. E. DAVIS, Assistant Examiner. 

